This invention relates to thermoplastic polyurethane elastomers (Hereafter TPUs). More particularly, this invention relates to a new class of TPUs prepared with poly(trimethylene carbonate) diol (PTMC diol) as the soft segment. The TPUs prepared using PTMC diols were extended with glycols, preferably lower functionality glycols, including, for example, 1,3-propanediol and 1,4-butanediol.
Thermoplastic polyurethane elastomers (TPU""s) are of technical importance because they offer a combination of high-quality mechanical properties with the known advantages of inexpensive thermoplastic processability. Much variation in mechanical properties can be achieved by the use of different chemical components. A survey of TPU""s, their properties and applications are discussed, for example in Polyurethane Handbook, Gxc3xcnter Oertel, Ed., Hanser Publishers, Munich, 1985, pp. 405-417.
TPU""s are built up from linear polyols, usually polyesters or polyethers, organic diisocyanates and short-chain diols (chain extenders). The overall properties of the TPU will depend upon the type of polyol, its molecular weight, the structure of the isocyanate and of the chain extender, and the ratio of soft and hard segments.
Polyurethanes may be either thermoplastic or thermoset, depending on the degree of crosslinking present. Both thermoset and thermoplastic polyurethanes can be formed by a xe2x80x9cone-shotxe2x80x9d reaction between isocyanate and polyol or by a xe2x80x9cpre-polymerxe2x80x9d system, wherein a curative is added to the partially reacted polyol-isocyanate complex to complete the polyurethane reaction. Thermoplastic urethanes do not have primary crosslinking while thermoset polyurethanes have a varying degree of crosslinking, depending upon the functionality of the reactants.
Thermoplastic polyurethanes are commonly based on methylene diisocyanate (MDI) or toluene diisocyanate (TDI) and include both polyester and polyether grades of polyols. For adjustment of the properties, the polyols, chain extenders, and diisocyanate components can be varied within relatively wide molar ratios.
For improvement of the processing behavior, particularly in the case of products for processing by extrusion, increased stability and an adjustable melt flow are of great interest. This depends on the chemical and morphological structure of the TPU""s. The structure necessary for an improved processing behavior is conventionally obtained by the use of mixtures of chain extenders, e.g. 1,4-butanediol/1,6-hexanediol. As a result of this the arrangement of the rigid segments is so greatly distorted that, not only is the melt flow improved, but simultaneously, the thermomechanical properties, e.g. tensile strength and resistance to thermal distortion, are often impaired.
The known TPUs and blends containing TPUs all suffer some drawbacks in one or more properties, including mechanical properties, color stability to heat and light, clarity, heat distortion properties, and phase separation. Attempts to improve one property, such as hardness, often lead to degeneration of another property.
Thus, problems exist in achieving hardness and related mechanical properties, stable color, clarity, and higher heat distortion temperatures in TPUs and blends containing TPUs. There is a need in the art to discover new formulations of TPUs that provide a broader range of mechanical and thermal properties without the degeneration of existing properties.
The present invention is useful in overcoming one or more problems with known thermoplastic materials by providing a new class of TPUs which provide new possibilities for mechanical and thermal properties in TPU formulations, including improvements in clarity, hardness, higher elasticity modulus, and improved softening temperature and coefficient of thermal expansion.
The present invention provides a new class of TPUs with improved properties and is based on poly(1,3-propanediol carbonate) diol (PTMC diol), with a hard segment comprising the portion of an isocyanate that reacts with a glycol plus the glycol blended into the TPU, and a diisocyanate to cure the system. The elastomers are somewhat harder than corresponding TPUs based on polyols known in the art. The PTMC TPUs exhibited good physico-mechanical properties, including somewhat higher elasticity modulus than a control TPU. The abrasion resistance and compression set was also very good, comparable to that of polyether TPUs. The softening temperature and the coefficient of thermal expansion was found to be improved over that of a control. In addition, using the PTMC polyol, it was possible to improve the clarity of the TPUs and in some examples even obtain completely clear material.
In accordance with the foregoing, the present invention comprises:
A new class of thermoplastic polyurethane elastomer (TPU) compositions which comprises:
a) A poly(trimethylene carbonate) diol (PTMC diol) as the soft segment;
b) A diisocyanate; and
c) At least one glycol (sometimes referred to as a chain extender) which reacts with the diisocyanate to form the hard segment which comprises from 10% to 55% by weight of the composition wherein the hard segment is defined as the sum portion of diisocyanate that reacts with the glycol plus the unreacted glycol.